i just read some reviews from http://hothardware.com/Articles/BFG-Ageia-PhysX-Physics-Card/?page=5
and as you cna see, there are MUCH more detail on the physics..... you bet !
But the FPS goes down, cause there are much more work to be done. The setup they used wasnt a GREAT gaming computer .. the test seems to be dating a bit.
But if your the kind off guy that want all the lill detail to be shown ! just go for physics card, or Link some more impressive Benchmark